1. Field of the Invention
The present invention relates to electrical musical instrument amplifiers, and more particularly to amplifiers of the type providing a tremolo effect, reverberation, and distortion mode operation when desired.
2. History of the Prior Art
Amplifiers designed for use with electrical musical instruments such as electric guitars are sometimes provided with the capability of producing certain effects in addition to the amplification of signals from the instrument to provide for driving a loudspeaker system. One desirable effect is that of tremolo or vibrato in which the music is made to sound as though it were coming from different directions by use of a technique similar to the Doppler Effect. Another common effect is that of reverberation in which the sound creates the impression of being reflected or echoing. Also, it is common practice in the case of electric guitars to increase the gain of the amplifier to produce operation in a distortion mode, thereby adding certain desired harmonics to the sound which are not other wise present.
The tremolo effect is presently obtained by using various circuit techniques including the use of a variable resistor or the use of a light dependent resistor modulated by a light and driven by an oscillator with the light dependent resistor being used to vary an amplifier. Such approaches have been accompanied by numerous problems, including problems in the circuitry itself and in the amount of circuitry required as well as in the quality of the tremolo effect which is achieved.
Reverberation is typically accomplished by feeding the signal from the instrument after it has been at least partially amplified in a preamplifier stage to a reverberation circuit where it is amplified and applied to a reverberation spring assembly. The spring assembly places transducers on opposite ends of a spring so as to delay the signal prior to sending it back to the preamplifier via a volume control for combination with the partially amplified signal in the preamplifier. In certain situations it may be desirable to adjust the volume control associated with the reverberation circuit to provide a very large reverberation signal. However where the output of the amplifier is set at a relatively high volume, and particularly where the reverberation spring assembly is located relatively close to the loudspeaker system which is typically the case, the reverberation spring undergoes vibration with a very bad effect on the resulting sound.
Operation in a distortion mode is usually accomplished by increasing the gain at the preamplifier stage to cause overdriving of the various stages thereof. However the most pleasing type of distortion usually results only when the gain at the power amplifier stage as well as at the preamplifier stage is turned up to a relatively high level. This enables the amplifier stages within the power amplifier to be overdriven, and the resulting sound in very satisfying, particularly where there are large power tubes in the power amplifier. However, as the gain of the power amplifier stages increases the resulting output waveform which begins to approach that of a squarewave provides an increasing duty cycle with the practical result that the power applied to the loudspeaker system is considerably greater. This may result in immediate destruction of the speaker system, but in any event results in a greatly shortened life for the speaker system in most cases. Consequently either an expensive speaker system must be periodically sacrificed to provide for a desirable distortion mode of operation, or the gain settings at the power amplifier stages must be left at low settings, thereby providing some distortion from the preamplifier but at the same time something less than the amount or quality of the distortion of this type usually desired.
Accordingly it would be desirable to provide an electrical musical instrument amplifier capable of providing an improved tremolo effect with a minimum addition of circuitry to the amplifier.
It would also be desirable to provide an electrical musical instrument amplifier in which the amount of reverberation and the total volume are automatically balanced so as to prevent inadvertent vibration of the reverberation spring and the resulting undesirable effects.
It would furthermore be desirable to provide an electrical musical instrument amplifier in which both the power amplifier stages and the preamplifier stages can be driven in a distortion mode whenever desired without damaging or greatly shortening the life of the speaker system.